In the production of commercial innerspring mattresses, a metal coil innerspring “core” is covered with padding and a fabric cover. An innerspring core generally includes a plurality of laterally spaced coil spring elements connected together in a rectangular array to form a spring mat.
At the present time, most of the metal coil innerspring cores are made at one location by a single manufacturer and then shipped to various other customer locations for incorporation in finished mattresses. Mattress manufacturers generally have their own brands, styles, technical specifications, and inner spring constructions to meet consumer's specific tastes.
Shipping of spring cores from the core manufacturer to the mattress manufacturers presents a challenge, because the spring cores are flexible and mostly air and take up a substantial amount of space. A process for shipping mattress cores has been developed and has been in use for many (at least twenty) years. However, the evolution of this process over time has created numerous problems that have existed for many years, and these problems are continuing to get worse.
The current process for packaging spring cores involves placing an average of twelve cores in alignment on their edges within a horizontal hydraulic press so as to form a bale. A single sheet of core separator paper (called “interleaving paper”) is positioned between each pair of spring cores in the bale in order to maintain the separation between adjacent spring core units when the cores are compressed together. Additionally, heavier laminated paper stock panels (referred to herein as “end panels”) are placed on the exposed outer sides of the bale. At this time, up to three employees puncture the unit from one side of the cores to the other using fifteen foot spears (up to 40 spears total) as fast as they can, aligning the spears through the same hole locations in each of the individual innerspring cores. Spearing the bale is a critical part of the process, because without the spears to guide and hold the spring cores in alignment, the cores would slip sideways out of alignment during compression. The bale is then compressed to about a fifteen inch thick sandwich and is held together using wood braces and/or tie wires or banding during transit. The baled “crate” is generally under about 18,000 lbs. of pressure, so the packaging is very critical.
For many years, there were no standard specifications for the interleaving paper placed between the individual innerspring cores or for the end panels placed on the outer sides of the stack of innerspring cores. As in any business, the cost of packaging can be a major concern, especially in such a high volume and packaging intensive product line as this. Therefore, at first many manufacturers would use the least expensive material available, often odd lot or rejected papers from other applications, which came in many different types and combinations. The result for the end converter (i.e., the finished mattress manufacturer) was inconsistency, product damage, and a generally unsafe working environment. It was not uncommon to find that when a bale was opened the interleaving paper was shredded into little pieces. This would cause the innersprings to become entangled and need repair if not rejected outright; both an added cost for the manufacturer. Likewise, substandard laminated cardboard used for the end panels would break, allowing the springs to jut out and become deformed, thereby damaging them as well.
Approximately twenty-five years ago, standard specifications were created detailing the requirements for the interleaving paper and end panels used in this application. In the original specification, around 1990, the end panels were specified as a lamination of two layers of heavy paper called “linerboard” (which is a type of heavy paper stock used in the manufacture of corrugated cardboard boxes) having a basis weight of 42 pounds per 1000 square feet (sq. ft.) per layer (which provides a total of 84 pounds per 1000 square feet for the two layers). The interleaving material was specified as a single layer of paper stock known as “natural kraft paper” (which is commonly used for wrapping paper, sandwich liner, and food packaging) having a basis weight of 50 lbs. per 3000 sq. ft. (about 17 lbs. per 1000 sq. ft.) (lighter kraft papers such as these are generally specified in nominal units of pounds per 3000 square feet).
Over the years, innerspring compression strength increased substantially, so it became necessary to increase the strength of the interleaving and end panel materials.
Around the year 2000, end panels were first increased from their original 1990 construction, wherein the end panel on each end of the stack consisted of two laminated plies of 42 lb. linerboard, to a construction employing two layers of the two ply 42 lb. linerboard at each end of the stack. This was later reduced to a three ply lamination of 42 lb. linerboard in 2010. Presently, a four ply 42 lb. linerboard end panel is being considered for specific units that are having higher than normal failure rates due to pressure-related rupture.
Interleaving materials likewise have increased in basis weight (heavier, stronger), first in 1995 from one layer to two layers (not glued) of natural kraft paper having a basis weight of 50 pounds per 3000 sq. ft. Then a single layer of 26 lb. per 1000 sq. ft. linerboard was substituted for the two layers of natural kraft paper in 2000. This was increased to two layers of 26 pound linerboard in 2010. The current specification is one layer of 33 lb. linerboard. One layer of 42 lb. linerboard is projected for the future.
The increased thickness of the end panels and interleaving has created two problems, first an increase in shipping costs due to the increased weight of packaging material used, and second, increased difficulty in piercing the end panels and interleaving layers prior to compressing the coil spring mattresses. The difficulties in piercing existing and future thicknesses of materials and the expense of the materials make it undesirable to continue to increase the thickness of interleaving sheets and end panels as spring compression strength continues to increase.
An object of the present invention is to provide improved end panels, extensible kraft paper laminates, and interleaving materials for packaging innerspring mattresses for shipping so as to facilitate packaging and reduce shipping costs.
Another object of the present invention is to provide an improved process for packaging compressed innersprings using the improved end panels and interleaving.